1. Field of the Invention
The present invention relates to a water-soluble cationic polymer dispersion produced by a specific process, and its use, especially in the waste water treatment as a flocculant, and in paper manufacturing as a paper chemical.
2. Background Art
Various types of processes have been utilized for the preparation of the aforesaid water-soluble cationic polymer. A stationary aqueous phase polymerization is a well-known process. Japanese Patent Laid-Open Application No.54-102388 discloses a water-in-oil type emulsion polymerization process. Japanese Patent Laid-Open Application No.54-69169 teaches a suspension polymerization process in a hydrophobic solvent.
There are a number of disadvantages associated with the known prior art processes such as those as set forth above.
In the stationary aqueous phase polymerization, it is necessary to employ a monomer concentration of more than 10% by weight in order to obtain a polymer having a suitable high-molecular weight.
The polymerization in such a higher monomer concentration gives a gelatinous hydrated polymer which is difficult to dissolve in the aqueous medium employed; therefore, it is necessary to ship the polymer product in a fluid form as a diluted solution after further dilution or in a powdered product after drying.
Shipment of the polymer in a diluted solution increases the costs of transportation, whereas shipment in a powdered form increases the cost of fuel for drying. Further, when heated in the drying process, three-dimensional crosslinking of the polymer may occur, yielding a partially water insoluble polymer.
The inflammability of the product as well as a wasteful use of expensive organic solvent are the drawbacks of the water-in-oil type emulsion polymerization process.
On the other hand, suspension polymerization in a hydrophobic solvent employs an inflammable solvent such as cyclohexane and toluene; therefore, plant investment costs are very high.
Japanese Patent Laid-Open Application No.50-70489 teaches a precipitation polymerization in an ammonium sulfate solution for the preparation of a nonionic or an anionic water-soluble polymer. The plant investment costs for the precipitation polymerization process are not expensive; however, the resulting polymer particles are sticky and have a tendency to agglomerate with each other to thereby give a large polymer mass which is not easy to handle.
Further, Japanese Patent Laid-Open Publication No.61-123610 (which partially corresponds to EP-A-0183466) proposes a process for the polymerization or copolymerization of a quaternary benzyl chloride salt of dimethylaminoethyl(meth)acrylate as a cationic monomer in which the polymerization is carried out in an aqueous salt solution which does not dissolve the resulting polymer or copolymer, and in the presence of a polymer which is soluble in the salt solution to thereby provide a cationic water-soluble polymer in a dispersed state. This proposal may be effective in solving problems associated with the known prior art processes as set forth above; however, the process has the disadvantage that the cationic monomer which can be used is limited only to the quaternary benzyl chloride salts of dimethylaminoethyl (meth)acrylate, and the like.
Accordingly, it is the principal object of the present invention to provide a novel cationic water-soluble polymer dispersion having the following features:
A. As the cationic monomer, the quaternary aliphatic halide salts of dimethylaminoethyl(meth)acrylate and the like is employed instead of the quaternary benzyl chloride salts. PA1 B. The dispersion polymer products having different hydrophobicity are easily prepared by changing the length of aliphatic chain. PA1 C. Several new characteristics could be obtained through this invention, which are valuable in the field application, such as higher floatation speed of the suspended particles (Example 4), improved sizing effect of rosin sizing agent with less addition of aluminum sulfate (Example 6), the enhanced sludge dehydrating and drainage property (Examples 5 and 7). (The details of such effects are explained in the referred examples.) PA1 D. The production is carried out in an aqueous solution in the absence of an inflammable solvent. PA1 E. The investment costs for the polymer dispersion is not expensive. PA1 F. The resulting polymer particles are not sticky, and have not a tendency of forming gel, therefore, the resultant dispersion may easily be handled. PA1 G. The resulting polymer dispersion has a good fluidity in high concentration level, thus decreasing the costs of transportation.
As a result, it is possible to provide a highly fluid dispersion of cationic water-soluble polymer having a greater hydrophobic property than that according to the technique disclosed in Japanese Patent Laid-Open Publication No.61-123610 (which partially corresponds to EP-A-0183466) by adopting the component of the present invention, thus improves substantially the operational performances in such application areas as waste water treatment and paper manufacturing.